Higher Degree Of Reduction Research Articles

Disruption of the Reductive 1,3-Propanediol Pathway Triggers Production of 1,2-Propanediol for Sustained Glycerol Fermentation by Clostridium pasteurianum.

Crude glycerol, the major by-product of biodiesel production, is an attractive bioprocessing feedstock owing to its abundance, low cost, and high degree of reduction. In line with the advent of the biodiesel industry, Clostridium pasteurianum has gained prominence as a result of its unique capacity to convert waste glycerol into n-butanol, a high-energy biofuel. However, no efforts have been directed at abolishing the production of 1,3-propanediol (1,3-PDO), the chief competing product of C. pasteurianum glycerol fermentation. Here, we report rational metabolic engineering of C. pasteurianum for enhanced n-butanol production through inactivation of the gene encoding 1,3-PDO dehydrogenase (dhaT). In spite of current models of anaerobic glycerol dissimilation, culture growth and glycerol utilization were unaffected in the dhaT disruption mutant (dhaT::Ll.LtrB). Metabolite characterization of the dhaT::Ll.LtrB mutant revealed an 83% decrease in 1,3-PDO production, encompassing the lowest C. pasteurianum 1,3-PDO titer reported to date (0.58 g liter(-1)). With 1,3-PDO formation nearly abolished, glycerol was converted almost exclusively to n-butanol (8.6 g liter(-1)), yielding a high n-butanol selectivity of 0.83 g n-butanol g(-1) of solvents compared to 0.51 g n-butanol g(-1) of solvents for the wild-type strain. Unexpectedly, high-performance liquid chromatography (HPLC) analysis of dhaT::Ll.LtrB mutant culture supernatants identified a metabolite peak consistent with 1,2-propanediol (1,2-PDO), which was confirmed by nuclear magnetic resonance (NMR). Based on these findings, we propose a new model for glycerol dissimilation by C. pasteurianum, whereby the production of 1,3-PDO by the wild-type strain and low levels of both 1,3-PDO and 1,2-PDO by the engineered mutant balance the reducing equivalents generated during cell mass synthesis from glycerol. Organisms from the genus Clostridium are perhaps the most notable native cellular factories, owing to their vast substrate utilization range and equally diverse variety of metabolites produced. The ability of C. pasteurianum to sustain redox balance and glycerol fermentation despite inactivation of the 1,3-PDO pathway is a testament to the exceptional metabolic flexibility exhibited by clostridia. Moreover, identification of a previously unknown 1,2-PDO-formation pathway, as detailed herein, provides a deeper understanding of fermentative glycerol utilization in clostridia and will inform future metabolic engineering endeavors involving C. pasteurianum To our knowledge, the C. pasteurianum dhaT disruption mutant derived in this study is the only organism that produces both 1,2- and 1,3-PDOs. Most importantly, the engineered strain provides an excellent platform for highly selective production of n-butanol from waste glycerol.

Mechanisms and Kinetics of Solid State Reduction of Titano Magnetite Ore with Methane

Sustainable development aims to reduce energy demand and carbon footprint in all fields of industry. In this study, a new approach to decrease these has been performed. Methane, a hydrocarbon gas, has been employed as a reductant with better reducing properties than solid carbon and hydrogen separately. Reduction of a titano magnetite ore has been executed at temperature ranging from 800 to 1200 °C using methane contents between 10 and 30 vol% in the hydrogen–methane gas mixture. Due to the high carbon activity reaching up to approximately aC = 200, higher reduction degrees has been achieved at lower temperatures compared to ordinary carbothermic reductions. Kinetically, the reduction of titano magnetite ore was most likely mix controlled regardless of the methane contents used. The reduction process especially at the early stages displayed shrinking core behaviour. The calculated activation energies, based on the obtained experimental metallisation data, varied when assuming the reaction is controlled by diffusion (iron 25–28 kJ/mol, titanium: 335–355 kJ/mol) or chemical reaction rate (iron 21–25 kJ/mol, titanium 178–184 kJ/mol) indicating a likely mixed control process. Iron was fully reduced at 1000 °C after 1 h and at 1200 °C in half an hour. The calculated rate constants for metallisation of titanium, vanadium and iron varied too, i.e. Fe from 0.00454 to 0.01150. The possible reduction mechanism is presented and discussed based on the kinetics results achieved and SEM–EDS observations.

Reduction Behaviour of Iron Ore–Coal Composite Pellets in Rotary Hearth Furnace (RHF): Effect of Pellet Shape, Size, and Bed Packing Material

Reduction of iron ore–coal composite pellets in multi-layers at rotary hearth furnace (RHF) is limited by heat and mass transfer. Effect of various parameters like pellet shape, size, and bed packing material that are supposed to influence the heat and mass transfer in the pellet bed, have been investigated, on the reduction behaviour of iron ore–coal composite pellets at 1250 °C for 20 min in a laboratory scale RHF. Reduced pellets have been characterised through weight loss measurement, estimation of shrinkage, porosity, and qualitative, quantitative phase analysis by XRD. A significant difference in the degree of reduction is observed layer-wise in the pellet bed with the variation in pellet shape and size. Pellet bed without any packing material or packed with coal have demonstrated higher degrees of reduction compared to the pellet bed packed with graphite and sand.

La1−xCexMnO3/attapulgite nanocomposites as catalysts for NO reduction with NH3 at low temperature

A series of attapulgite (ATP) supported perovskite-type La1−xCexMnO3 (x=0–0.2) nanocomposites were prepared by a sol–gel method. The samples were characterized by X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, H2 temperature-programmed reduction, and temperature-programmed desorption of NH3. Their selective catalytic reduction of NO with NH3 was evaluated in the low-temperature range. The impact of the doping fraction of Ce4+ on the NO conversion was investigated. The results indicated that the La1−xCexMnO3 nanoparticles with a size of ca. 15nm were uniformly immobilized on the surface of ATP with a loading amount of 20wt%. The highest conversion rate of NO reached 98.6% when the doping fraction x was 0.1, while the ATP support supplied a high surface areas facilitating the nanoparticles dispersion as well as the gas adsorption. Incorporation of an appropriate amount of Ce4+ in the La3+ site resulted in a high degree of reduction by the active perovskite species with enhanced catalytic activity.

Investigations into enhanced wax production with combustion synthesized Fischer–Tropsch catalysts

Combustion synthesized (CS) cobalt catalysts deposited over two supports, alumina and silica doped alumina (SDA), were characterized and tested for its Fischer–Tropsch (FT) activity. The properties of CS catalysts were compared to catalysts synthesized by conventional impregnation method (IWI). The CS catalysts resulted in 40–70% increase in the yield of C6+ hydrocarbons compared to IWI catalysts. The FT activity for CS catalysts showed formation of long chain hydrocarbon waxes (C24+) compared to the formation of middle distillates (C10–C20) for IWI synthesized catalysts, indicating higher hydrocarbon chain growth probability for CS catalysts. This is ascribed to the smaller crystallite sizes, increased degree of cobalt reduction and consequentially, a higher number of active metal sites exposed over the catalyst surface. Additionally, 12–13% increase in the overall C6+ hydrocarbon yield is realized for SDA-CS catalysts, compared to Al2O3-CS catalysts. The improved performance of CS-SDA catalysts is attributed to 48% increase in cobalt dispersion compared to Al2O3 supported CS catalysts, which is again caused by the decrease in the cobalt-support interaction for SDA supports. The metal support interactions were analyzed using XPS and H2 TPR–TPD experiments. Combustion method produced catalysts with smaller crystallite size (17–18nm), higher degree of reduction (∼92%) and higher metal dispersion (16.1%) compared to the IWI method. Despite its enhanced properties, the CS catalysts require prominently higher reduction temperatures (∼1100–1200K). The hydrocarbon product analysis for Al2O3 supported catalyst showed higher paraffin wax concentrations compared to SDA supported catalysts, due to the lower surface basicity of Al2O3. This work reveals the impact of the CS catalysts and the nature of support on FT activity and hydrocarbon product spectrum.

Experimental and Theoretical Study on the Electronic Interaction between Rh Adatoms and CeOx Substrate in Dependence on a Degree of Cerium Oxide Reduction

The electronic metal–substrate interaction plays an important role in the surface reactions on supported metal nanoparticles. We study the interaction between rhodium clusters and cerium oxide substrate having various stoichiometries, CeOx (2.00 > x > 1.67), by means of photoelectron spectroscopy. Our results show that rhodium deposited on substrates with stoichiometry of 2.00 > x > 1.93 induces reduction of cerium oxide. On the other hand, cerium oxide with a higher degree of reduction (1.93 > x > 1.67) becomes partially oxidized after the Rh deposition. Density functional theory simulations of Rh adatom adsorbed on the CeO2(111) surface and on an oxygen vacancy at the CeOx(111) surface show that there is a charge transfer between rhodium and cerium oxide substrate. While Rh adsorption on the CeO2(111) surface leads to electron depletion at the Rh adatom and cerium oxide reduction, Rh adsorption on the oxygen vacancy at CeOx(111) leads to electron accumulation about the Rh adatom and partial oxidation of...

Preparation of a high performance cobalt catalyst for CO2 reforming of methane

The novel silica supported cobalt catalysts powders promoted by ruthenium and zirconium (CRZS) were prepared via a coprecipitation method for the catalytic CO2 reforming. The optimum metals loadings and pH of solution were systematically investigated in order to obtain a high performance and coke resistant catalyst. The most active, stable, and coke resistance catalyst was found in the catalyst prepared at pH 1 with the combination of 14.68wt.%, 0.14wt.%, 5.00wt.%, and 80.00wt.%, respectively for cobalt, ruthenium, zirconium and silica. BET, XRD, TPR, and H2 chemisorption analyzer found that the phenomena of Co3O4 cluster enlargement as the increase of cobalt loadings, the higher reduction degree and pore diameter as the increase of ruthenium loadings, and the inhibition of strong Co–SiO2 interaction in the proper zirconium loading were confirmed as the variation of metals loadings. The variable of pH solution during catalysts preparation gave significant effects on the catalysts stability and coke formation. The deactivation of catalyst prepared in low pH was related with the presence of surface ZrO of catalyst without any relation with coke formation. The obtained parameters of methane consumption rate based on Eley–Rideal mechanism showed that the surface chemical reaction between methane and surface oxygen became the rate-determining step of the reaction.

Effect of Axial and Torsional Vibrations on Tapping Performance

Abrupt breakage of the taps is frequently encountered during tapping threads, especially when tapping on ‘difficult-to-cut’ material like titanium. This work therefore presents an extensive experimentation with the Taguchi approach to investigate maximum torque in tapping on titanium alloys while performing axial and, axial and torsional vibration-assisted tapping (AVAT and ATVAT). The experimentation shows that both AVAT and ATVAT reduce the tapping torqueduring tapping as compared to that of in conventional tapping process. However, ATVAT process had exhibited a higher degree of reduction in torque when compared to AVAT process.

Nickel-based catalysts: Dependence of properties on nickel loading and modification with palladium

The aim of this study was comparative analysis of catalysts with 5 and 20 wt. % Ni loading, with and without Pd additive, and it included: determination of reduction degrees, investigation on microstructure by scanning electron microscopy and chemical analysis by energy-dispersive spectroscopy. Ni/Al2O3 and Ni-Pd/Al2O3 catalysts supported on ?-Al2O3-based foams were synthesized by aerosol assisted impregnation. Impregnation of the foams by ultrasonically aerosolized chlorides was followed by drying at 473 K and hydrogen reduction at 533 and 633 K. Lower Ni loading resulted in higher reduction degrees. Ni loading of 20 wt. % enabled relatively uniform coverage of the foam with a metallic coating. With activity modifier (Pd), nearly complete reduction was achieved at both temperatures. Reduction degrees reached 99.4 and 98.2 wt. % at 533 K for 5 and 20 wt. % of Ni, respectively.

Macroanatomical aspects of the gastrointestinal tract of the alpaca (Vicugna pacos Linnaeus, 1758) and dromedary (Camelus dromedarius Linnaeus, 1758)

Although camelids and taxonomic ruminants share fundamental convergent properties, such as microbial fermentation and a sorting mechanism in the forestomach with a resulting high degree of digesta particle size reduction, there are important differences in the capacity to process high amounts of food. We describe qualitative and quantitative characteristics of the gastrointestinal anatomy of alpacas (Vicugna pacos, 44.4 ± 5.5 kg body mass), supplemented with some observations in dromedaries (Camelus dromedarius). The long large intestine of alpacas (610 ± 128 cm) corresponds to the adaptation of camelids to arid environments. An important difference to taxonomic ruminants is the position of the second forestomach compartment (C2 vs. reticulum), which is not in line of the major forestomach axis in camelids, and the size of the corresponding orifice (C1-C2 vs. Ostium rumino-reticulare), which is distinctively smaller in camelids (alpaca: 3.2 ± 0.3 cm width × 4.2 ± 0.3 cm height, dromedary: 8.5 ± 0.7 cm diameter) as compared to literature data for similar-sized ruminants. The opening between the second and third forestomach compartment (C2-C3 vs. Ostium reticulo-omasale) is of similar magnitude in camelids (alpaca: 2.2 ± 0.7 cm diameter, dromedary: 3.1 ± 0.5 cm diameter) and ruminants, but is opposite to the C1-C2 opening in camelids in a dorsal position. The generally smaller opening might represent a reason for the generally lower food processing capacity in camelids, and together with the arrangement of the openings might result in conditions during contractions of the C2 that are more favourable to (a low proportion of) larger particle escape into the C3. In contrast, the different arrangement of the openings and the larger connection to the preceding chamber might make such an escape of (a low proportion of) large particles from the reticulum to the omasum less likely in ruminants, giving their sorting mechanism a clear-cut anatomical threshold in the Ostium reticulo-omasale.

The effect of reduction degree of GO nanosheets on microstructure and performance of PVDF/GO hybrid membranes

In this study, the effect of the reduction degree of GO nanosheets on the microstructure and performance of PVDF/GO membranes were systematically investigated via comparing four PVDF/GO membranes synthesized by the casting solutions prepared at 50, 70, 85 and 100°C, which were denoted PVDF/GO-50, PVDF/GO-70, PVDF/GO-85 and PVDF/GO-100, respectively. X-Ray Photoelectron Spectrometer (XPS) and Raman Spectroscopy results showed that the preparation temperature of the casting solution affected the reduction degree of GO nanosheets. Higher preparation temperature resulted in a higher degree of reduction. Compared with the pure PVDF membrane, PVDF/GO membranes achieved better performance in term of membrane flux and rejection. However, the optimal loading of GO nanosheets was dependent on the reduction degree. For the PVDF/GO-50 membrane, the maximal membrane flux (46L/m2h) was reached at a GO loading of 0.5%, while the membrane flux of the PVDF/GO-100 membrane increased with GO loading in the range of 0–2%. SEM and AFM characterization results also showed that both GO loading and reduction degree of GO influenced the pore structure and surface roughness of PVDF/GO membranes. It is worth noting that the mechanical strength of the PVDF/GO membranes was weaker than that of the pure PVDF membrane at all GO reduction degrees regardless GO loading. This indicates that the integrity of PVDF membranes might be impaired by GO nanosheets.

Briquette Smelting in Electric Arc Furnace to Recycle Wastes from Stainless Steel Production

Wastes from stainless steel production were briquetted together with carbon for smelt-reduction in the electric arc furnace, EAF, to achieve an internal recycling. A laboratory induction furnace was used to simulate the EAF. With a close simulation of the smelting, disintegration of the briquettes heated under load and recovery of metals from briquettes melted together with stainless steel and slag former were investigated. The influences of test conditions on carbon reduction of oxides in the briquettes were also examined. The briquettes endured heating at 1 186 °C under load of 3.5 kg and could be charged to the melt in small quantity without causing serious splashing. For a high metal recovery, it was necessary to charge the briquettes together with slag former. Small local zones of smelt-reduction with high carbon concentration could thus be formed during the charger heating. Silicon content in the metal near to the briquettes should be minimised to achieve a high degree of carbon reduction. Based on results obtained from this study, suggestions were made on smooth operations of smelt-reduction of the briquettes by using EAF or induction furnace with large scales.

Enhanced photocatalytic activity of a TiO2/graphene composite by improving the reduction degree of graphene

Two kinds of graphene prepared by a high-temperature exfoliation and a solvothermal method were used as supports of a TiO2 catalyst (P25) from Degussa, Inc to prepare TiO2/graphene composites. The photocatalytic activities of the composites were evaluated by their degradation of Rhodamine B in aqueous solutions under visible light. Results indicate that the composites prepared by high-temperature exfoliation have much higher photocatalytic activities than those produced by the solvothermal method or the unsupported P25. Both the adsorption capacity of Rhodamine B on the composites and their light absorption characteristics are independent of the kind of graphene used. The activity increases with exfoliation temperature and reduction degree of the graphene regardless of the methods and conditions used, indicating that a high degree of reduction of graphene can inhibit the recombination of electron-hole pairs generated by light irradiation by increasing electron transfer from TiO2 to the graphene layer.

Steam CO2 reforming of methane over La1−xCexNiO3 perovskite catalysts

Steam CO2 reforming of methane was carried out over cerium substituted perovskite catalysts. Among the catalysts studied, La0.9Ce0.1NiO3 showed the best performance with 49% of methane and 14% of CO2 conversion under the tested conditions. The chemical and structural properties of the catalysts before and after the reaction were studied by N2 physisorption, X-ray diffraction, CO2-TPD, TPH, TPR, TGA and TEM. It was found that most of Ce existed as CeO2 rather than being incorporated in perovskite lattice because of large difference in ionic radii between La3+ and Ce4+. Few substitution of Ce in A site resulted in high degree of reduction for active Ni species with good catalytic activity which was further decreased with increasing Ce concentration; substitution of large amount of Ce species led to methanation of CO2 and formation of large nickel cluster. TPH and TGA analysis revealed that Ce substituted catalyst has better resistance to coke deposition compared to non-promoted perovskite catalyst.

Co-pyrolysis of biomass tar and iron ore fines for the production of direct reduced iron

Biomass tar can be used as reducing agent for reduction of iron oxide, and simultaneously iron is a good catalyst for tar cracking. Thus, an iron ore reduction system integrated tar cracking and iron ore reduction was proposed. The influences of raw material characteristics, the equivalence ratio of tar to iron ore fines as well as reduction conditions on the reduction behaviors of iron ore fines were discussed. Also, the co-pyrolysis of mixture of tar and iron ore fines was investigated. The results show that the iron ore reduction using tar is reliable with a high tar cracking efficiency and a high reduction degree. Due to the formation of porous structures, preheated iron ore fines showed an excellent reduction behavior than those without preheating. At the initial stage, iron oxide did not exert any obvious effect on tar destruction, while as reaction temperature raised above 600 °C, a noticeable decline of tar content was observed, which was attributed to the enhanced reduction consumption and catalytic decomposition by the reduced iron. Increasing the ratio of tar to iron ore was favorable for the reduction of iron oxide, while, when the ratio exceeding 0.6, the effect became less notable. The introduction of proper amount of steam can improve tar cracking and further improve iron oxide reduction. At optimum conditions (iron ore fines was first preheated at 400 °C and then mixed with tar according to tar/iron ore fines 0.6, reacted at 900 °C for 30 min under the steam atmosphere with the mass ratio of steam/tar 0.87), the reduced iron product with metallization rate 94.1% was achieved.

Reduction kinetics of iron oxide pellets with H2 and CO mixtures

Reduction of hematite pellets using H2-CO mixtures with a wide range of H2/CO by molar (1:0, 3:1, 1:1, 1:3, and 0:1) at different reducing temperatures (1073, 1173, and 1273 K) was conducted in a program reducing furnace. Based on an unreacted core model, the effective diffusion coefficient and reaction rate constant in several cases were determined, and then the rate-control step and transition were analyzed. In the results, the effective diffusion coefficient and reaction rate constant increase with the rise in temperature or hydrogen content. Reduction of iron oxide pellets using an H2-CO mixture is a compound control system; the reaction rate is dominated by chemical reaction at the very beginning, competition during the reduction process subsequently, and internal gas diffusion at the end. At low hydrogen content, increasing temperature takes the transition point of the rate-control step to a high reduction degree, but at high hydrogen content, the effect of temperature on the transition point weakens.

Effects of reduction methods on the structure and thermal conductivity of free-standing reduced graphene oxide films

In this work, free-standing graphene oxide (GO) films obtained by vacuum filtration were reduced in HI acid or annealed in a confined space to form self-standing reduced graphene oxide (RGO) films. The effects of reduction methods on the reduction degree, microstructure and thermal conductivity of the RGO films were investigated. The RGO films obtained by thermal annealing have higher reduction degree than those treated with HI acid (55%) or treated with the combination of HI acid and 600°C annealing. The X-ray pole figure measurements show that the orientation degree of GO films after reduction is degraded, and the HI acid reduction results in the worst oriented structure. The in-plane thermal conductivities of the RGO films obtained by thermal reduction are higher than those of films reduced by other methods due to their higher reduction degree and the resulting unfolded structure. However, the differences in the thermal conductivity of the RGO films obtained by thermal annealing at different temperatures are minor, even their reduction degree is enhanced with the increasing of annealing temperature, which is probably due to the generated interspaces between the graphene layers during reduction that greatly limit thermal transport.

Performance analysis of an adaptive feedback active noise control based earmuffs system

This paper analyzes the performance of the adaptive feedback active noise control (FBANC) based earmuffs system. The system’s noise reduction performance is obtained in a closed-form equation with respect to two top-level design constraining parameters, i.e., secondary path delay and noise bandwidth. To derive the equation, we utilize a simplified and equivalent linear prediction ANC model and parameterize noise bandwidth using an autoregressive model. The derived equation is validated by simulations and experimental tests performed for the ANC earmuff system. The high degrees of noise reduction, which are 14.9dB for the airplane noise and 20.4dB for the house heater noise, obtained from the experimental tests confirm the feasibility of the ANC earmuffs application.

Easy preparation of ultrathin reduced graphene oxide sheets at a high stirring speed

This work explored the synthesis of rGO sheets from graphene oxide (GO) using hydrazine solvent as reducing agent through chemical reduction. Meanwhile, GO films with a 2D structure were prepared from graphite flakes (starting material with an average flake size of 150nm) by an Improved Hummer׳s method. Results showed that the chemical oxidation of graphite flakes carried out at room temperature could be used to prepare GO sheets in the initial stage. The conversion of GO into large-area rGO sheets with ~85% of carbon content could then be achieved by chemical reduction. RGO sheets with a lateral dimension of up to ~45nm were obtained, which indicated the formation of an extremely thin layer of rGO sheets. A high degree of GO reduction was also realized using a high stirring speed (1200rpm) for 72h in a mixture of acids and potassium permanganate, resulting in a high carbon content of rGO with a large lateral dimension and area. Overall, our Improved Hummer׳s method with a high stirring speed (1200rpm) for 72h provided an easy approach to the preparation of large-area and ultrathin rGO sheets.

Эволюция кристаллографической текстуры в титановом сплаве ВТ6, подвергнутом плоской прокатке

This work presents the results of experimental studies and computer modeling of the crystallographic texture evolution in the billets of titanium alloy VT6, subjected to plane rolling in the coarse-grained and ultrafine-grained (UFG) states. UFG state has been formed by the method of multiaxial isothermal forging at 650°С with the number of cycles equal to 6. Plane rolling was performed until the reduction equal to 75% and 95% at 550°С. The analysis of pole figures revealed that plane rolling of UFG state, unlike in the coarse-grained state, promotes the orientation of grains with basal plane substantially parallel to the rolling plane. Modeling of pole figures within the viscoplastic self-consistent model, implemented in the Voce framework, allowed to determine the active slip and/or twinning systems depending on the reduction at plane rolling. It is shown that prismatic slip system, tensile and compression twinning systems are the most active systems at plane rolling of the investigated alloy in the coarse-grained state. At the same time, the dislocation activity of the basal and pyramidal <a> slip systems is observed at high degrees of reduction at plane rolling. In the case of UFG state, prismatic, pyramidal <a+c> of the first order and the basal slip systems are active. The processes of tensile and compression twinning are also implemented in initial stages of plane rolling, but their activity is rather low at high degrees of deformation.